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LESSON 8:

What you will need: • Data projector and internet access. • The Infinity Series Part 2: Deep Space - The dance of Gravity video. • A copy of the handouts for each student

Suggested Outline: • Hand out Skyways pg 61, 62

• Hand out and work through the following Ioncmaste: 9th Grade Astronomy Curriculum Resources webpage, Module 2 - #1 through 10. Use the applets provided on the website throughout. This works best on a data projector. If you do not have a data projector you may have to forgo using the applets and teach the lesson from the handouts alone. http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/files/h tml/module2/module2.html#6

• When discussing #3 “Types of Stars” o Hand out file “#8 - Types of Variable Stars” taken from the AAVSO website. (http://www.aavso.org/vstar/types.shtml)

o Discuss the different types of variable stars (use applet) Intrinsic: Pulsating, Eruptive Extrinsic: Eclipsing Binary, Rotating

o For more detailed variable info and information on how to start observing them the students should go to the AAVSO website. http://www.aavso.org/

o Point out AAVSO Manual available from AAVSO website. http://www.aavso.org/publications/manual/

• When discussing #4 “Temperature and Colours of Stars” o Have students do Skyways HR Diagram activity (pg 72, 73)

o Discuss stellar classifications (Oh, Be, A, Fine, Gal/ Guy, Kiss, Me) Show file “#6 – OBAFGKM chart” or use overhead provided.

o Hand out Skyways pg 74, 75

• When discussing #6 “The Life Cycle of a Star” o use the “Balloon Stars” demo from Skyways pg. 63 to help illustrate a star in equilibrium

• Watch The Infinity Series Part 2: Deep Space - The dance of Gravity video (First part only, about 40 min). The video discusses , quasars, pulsars, and a bit of cosmology.

Between Class Assignments: o Read Beginner’s Observing Guide chapter 7 and 16 Information about the Brightest Stars Observing Variable Stars

o Observe from ETUC Double & Multiple Stars and Variable Stars sections. The Brightest Stars The Nearest Stars

Star Power Temperature Star Power Temperature log(L/Lsun) degrees Celsius log(L/Lsun) degrees Celsius

Sun 0.00 5,840 0.00 5,840 3.15 7,400 A 0.18 5,840 A 0.88 6,580 Alpha Centauri B -0.42 4,900 2.84 20,500 -4.29 2,670 Altair 1.00 8,060 Barnard's Star -3.39 2,800 1.11 9,060 HD 93735 -2.30 3,200 Dened 4.76 9,340 UV Ceti (B) -4.48 2,670 A 1.34 9,620 Sirius B -2.58 14,800 1.72 9,900 -4.01 2,670 4.16 3,200 -3.49 2,800 Hadar 4.00 25,500 GX Andromedae -2.26 3,340 3.96 3,340 -0.90 4,130 2.20 13,260 Wolf 359 -4.76 2,670 Adhara 3.96 23,000 L726-8 (A) -4.28 2,670 Bellatrix 3.60 23,000 Sirius A 1.34 9,620 Alnilam 4.38 26,950 Ross 154 -3.36 2,800 Alpha Crucis B 3.22 20,500 -0.56 4,590 Al Na'ir 2.34 15,550 L789-6 -3.90 2,670 Elnath 2.54 12,400 GQ Andromedae -3.45 2,670 Alhena 1.90 9,900 A -1.12 4,130 +6 S

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Student Handouts

Module 2: The Sun and Stars

Background Information

1. Introduction to Stars 6. The Life Cycle of a Star 2. Brightness of Stars 7. Composition of Stars

3. Types of Stars 8. The Surface of the Sun 4. Temperatures and Colours of Stars 9. Studying the Sun and Stars 5. Spectrum of Light 10. Summary

1. Introduction to Stars

Our star is a ball of gas that produces energy in its core by means of nuclear reactions. These nuclear reactions process billions of kilograms of every second, producing enormous amounts of energy in the form of heat and light. The Sun, despite being a typical star, appears much brighter than all other stars simply because it is so close to us. Other stars are located so far away that their distances from the can be very difficult to grasp. A helpful analogy for understanding this concept is to imagine the Earth as a grain of sand with the Sun situated a metre away, leaving the nearest star some 270 kilometres away. The farthest stars visible with the naked eye would be located almost half a million kilometres away from that small speck of sand. There are also millions of other stars even farther away. Light from the Sun takes about eight minutes to reach the Earth, about 4.3 from the nearest star, and hundreds of years from the most distant visible stars. Stars are extremely bright and massive objects, but they are so incredibly distant that they appear as mere points of light in our sky.

2. Brightness of Stars While the thousands of stars in the night sky appear to be very similar, they are more distinct from one another than their appearance would suggest. Stars have various sizes, , temperatures, colours, , compositions and lifecycles. The largest stars are several hundred times the diameter of the Sun, and in our , would easily engulf the Earth’s orbit, while the smallest stars are smaller than the Earth itself. The most noticeable distinction between stars, however, is the difference in their brightness. The apparent brightness of an object in the sky is denoted by its magnitude, a numeric scale established by Hipparchus c. 160 BC. The brightest stars in the sky, Hipparchus stated, were of first magnitude, and the dimmest were of sixth magnitude, making smaller numbers correspond to brighter objects. The scale has been expanded and can now be applied to any object in the sky. The full moon has a magnitude of -12.7, Venus at its brightest is -4.1, the brightest star is -1.46 and the faintest objects detectable through the largest are about +29. Magnitude values are logarithmic, where a difference of five magnitudes is defined as a brightness differential of 100 times. The Sun and the dimmest objects detectable through telescopes are about 56 magnitudes apart, but this corresponds to an actual difference in brightness of over 25 x 1021.

Load Applet Stellar Magnitudes

3. Types of Stars

Binary courtesy Brian Martin

Most of the stars in the sky are double stars, which are pairs of stars located in nearly the same position in the sky. The two stars that make up a double star may not actually be close to each other in space, but simply lie in the same line of sight from the Earth. They usually appear as a single point of light because they are so closely aligned, so cannot be seen as individual stars unless viewed through a . Systems of double stars that are gravitationally bound and are in orbit around each other are called binary stars. Binary stars are often so close together they are only perceivable as two stars by analyzing their combined light. Binary stars are very common, the Sun being rare in that it is not part of a binary system. There are also a few individual stars that vary in their apparent brightness as seen from Earth, called intrinsic variable stars. The time period of the change in intensity of variable stars can be erratic or can be very regular, ranging from days to years.

Data Sheet

Load Applet Variable Stars

4. Temperatures and Colours of Stars

Sunrise over the Pacific Ocean courtesy David Vandervelde

Stars are classified by their temperature, which will affect their colour. The stars range in colour from red through yellow and white to blue. The Sun’s yellow surface is about 5800K (), while some red stars are 3000K and blue stars can have surface temperatures of over 30 000K. When we look up at the stars, they all appear to dazzle bright white, but many stars actually do have colour imperceptible to our eyes. The human eye is not sensitive to colours at low light intensities like those of the stars. When we use a telescope to look at the stars, they appear brighter and the colours become noticeable. allows for a more detailed classification system using the chemical composition of stars. The light emitted by stars can be broken down into the component colours at various . The spectrum will depend primarily on the star’s temperature, but it will also contain absorption lines which characterize the elements present in the star. Dark bands appearing along the spectrum will indicate the presence of specific elements, and their abundance will affect the width of the band. A spectrum is like a fingerprint and will reveal the chemical abundance within the star. 5. Spectrum of Light

White light is composed of a mixture of colours, but appears white because our eyes are unable to perceive the individual colours of the spectrum. It is possible to prove this phenomenon by separating a beam of white light into its component colours using a prism. These component colours are displayed in the colours of the rainbow, ranging from red to violet. The difference between the colours is in the of the light; red light has a higher wavelength than violet, with the remaining colours lying between those two extremes. Although the spectrum of light as seen in a rainbow is only a small portion of the entire electromagnetic spectrum, the human eye is sensitive only to the range of wavelengths from red to violet.

There are three types of spectra:

1. Emission Spectra - The light produced by a cool glowing gas can be seen through a spectrometer as a series of bright coloured lines. 2. Continuous Spectra - The light produced by heating a solid, liquid or gas to a high pressure can be seen through a spectrometer as a continuous spectrum. 3. Absorption Spectra - The light produced by heating a solid, liquid or gas to a high pressure that then passes through a cooler gas cloud, can be seen through a spectrometer as a continuous spectrum with dark lines.

Load Flash Applet Spectroscopy and Stellar Identification

6. The Life Cycle of a Star

Although it was previously thought that stars were static, never changing or evolving, we now know that stars move through a complex life cycle – they are created, live extremely long lives and then expire. It is, however, impossible to witness the entire life cycle of an individual star because it is an exceptionally lengthy process by human standards. By studying different stars in various stages of development, have now established a detailed process for their life cycle.

Stage 1 Stars form in cold, dark clouds of gas and dust. The cloud must be relatively cold for stars to form because the particles must be moving slowly enough to allow gravity to overcome internal pressure and form clumps of matter. The interstellar cloud must also be truly immense, covering billions of kilometres, and must be reasonably dense with and atoms for a star to form. It is thought that a shockwave from a nearby star will trigger a collapse of the cloud, after which the atoms slowly draw together due to the gravitational attraction between them. As the cloud shrinks, it breaks up into smaller fragments known as protostars. An initial interstellar cloud can produce hundreds of protostars. A protostar is a star in its embryonic stage, and although it glows due to the release of gravitational energy, it is not yet hot enough to produce nuclear reactions within its centre. As the protostar continues to collapse due to gravity, it will attract more atoms and continually increase in mass and density. The increased density and gravity will cause the core temperature to eventually rise to about ten million Kelvin, hot enough to convert hydrogen into helium (). Millions of years after the interstellar cloud first began to collapse, a star is created.

Stage 2

The young star will gradually continue collapsing until the internal pressure pushing out (caused by heat) equals the inward pull of gravity. This occurs when the central core temperature has increased to about 15 million Kelvin. The star is now in equilibrium, and will continue to process hydrogen for most of its life. This stable period of the star’s life will not end until the core becomes depleted of hydrogen, which can vary between millions and billions of years. The Sun, presently in its equilibrium phase, is converting billions of kilograms of hydrogen into helium every second, and will not exhaust its supply of hydrogen for about another four . The characteristics of a star are determined by its mass, which will depend on the size of the initial fragment of the interstellar cloud. While in its stable core hydrogen-burning phase, higher mass stars process their fuel of hydrogen (and produce more energy) at a much faster rate than low mass stars. As a result, massive stars burn hotter and brighter, have shorter lifetimes, and will typically have a larger radius. Once the core of a star begins to exhaust its reserve of hydrogen, the star quickly becomes unstable and will evolve from its state of equilibrium. The core is now packed with helium, and a thin spherical shell surrounding the core will begin to process hydrogen. This causes the core to become increasingly dense while the outer layers of the star will expand and cool. The gases will glow red and the star becomes a red giant. The hydrogen- burning shell will move outward from the core as it converts the hydrogen into helium, and the core will become progressively compact with helium. This increased pressure will raise the temperature of the core, and will eventually become hot enough to ignite nuclear reactions involving helium. The star now enters another period of equilibrium, and will spend another several million years converting helium into carbon.

Data Sheet

Stage 3a.

The most apparent difference between high mass (10 to 30 solar masses) and low mass (0.5 to 10 solar masses) stars are the events leading up to the eventual death of the star. Low mass stars do not have the mass required to increase the core temperature enough to allow the carbon to fuse into heavier elements. Once the helium is consumed, the star will die quietly by ejecting its outer layers, creating a planetary . The central carbon core of the star is left behind and continues to shine by stored heat. This remnant is called a white , and is about the size of the Earth, but is much more massive and incredibly dense. It will cool and dim with time as its stored heat is used up, and the star will become a cold and dark black dwarf, ending the star’s evolution. When a is part of a binary system with a red giant, its gravity will suck surface material off the red giant. Large amounts of matter falling into the white dwarf will cause instabilities, and explosions will occur in order to release the accumulated material. These explosions are called novae, and the white dwarf star will brighten significantly as seen from the Earth. A will last for about one week and then slowly die off and return to its previous brightness.

Data Sheet

Stage 3b.

High mass stars die much more dramatically, in violent explosions. In contrast to a low mass star, a high mass star has enough mass to continually increase the pressure and temperature of its core, which causes a chain of nuclear reactions involving heavier and heavier elements. The nuclear reactions eventually produce iron, but iron nuclei are so compact that they do not release energy in nuclear reactions and produce no heat. With the end of energy production in the core, it no longer produces enough heat to generate adequate inner pressure to match the enormous gravitational pull. At this stage the core is so incredibly dense that it cannot collapse any further and the state of equilibrium comes to an end. The inner core sucks in the surrounding layers and the star will implode and collapse in on itself in a matter of seconds. The material of the collapsing star rebounds off the solid core, producing a shockwave of material that explodes into space. This explosion is called a supernova, and will increase the of the star by a factor of millions. A supernova is much more powerful than a nova and will be extremely bright for a few weeks or months, until it gradually subsides and dims. What remains after a supernova explosion is called a supernova remnant, the star’s outer layers that were blasted into space during the supernova. The gases expand out from the star at incredible speeds and excite the gaseous atoms of the , causing it to glow as a nebula. Depending on the initial conditions of the star, what is left will become either a neutron star*, a black hole, or could simply blow itself completely apart, leaving only the remnant.

* Note that if the neutron star is rotating very rapidly and is oriented so that the pulses of energy are aligned with the Earth it can be called a pulsar.

Data Sheet

The time frame for the death of a high mass star is extremely short. While the hydrogen-burning phase lasts for millions of years, the final stages of a star’s life leading up to a supernova last for progressively shorter periods, culminating in the core collapse and explosion which last mere seconds. Because the death of a star occurs so rapidly, we can directly witness the process. Thus, supernovae reveal valuable information about stars and our universe. The death of stars is an important part of the stellar life cycle because it promotes star formation. The explosions produce shockwaves that can trigger the collapse of an interstellar cloud into a protostar. Stars also eject their outer layers into space, which produces an interstellar cloud rich in hydrogen and helium atoms. Supernovae release huge amounts of heavy elements into the interstellar medium, which produces perfect conditions for the birth of a star with rocky planets like our solar system. Without the death of stars, it would be very difficult for new stars and solar systems to form.

Data Sheets

Load Flash Applet Life of a star applet

Load Star Age Calculator Star Age Calculator

Life Cycle of a Star

Low Mass Stars (like Sun)

1. Star forming region 2. Protostars 3. Sun-like star 4. Red Giant

5. Planetary Nebula 6. White Dwarf

High Mass Stars

1. Star forming region 2. Protostars 3. High mass stars 4. Red Super Giant

5. Supernova explosion* 6. Supernova remnant 7a. Neutron Star 7b. Black Hole

7. Composition of Stars

In composition and size, the Sun is an average star and is in the middle of its hydrogen-burning stage. It will continue to process hydrogen for another few billion years before swelling into a red giant. Although the Sun is an average- sized star, it is still huge by Earthly standards, having a diameter more than 100 times that of the Earth and a volume nearly 1.3 million times as great. The Sun is a ball of gas, and as such does not have a surface like the Earth. The “surface” of the Sun is called the , and is where energy from the core is emitted into space. The photosphere has a definite sharp edge as seen from the Earth, but its granular appearance is constantly “bubbling” as heat from the interior escapes into space. Above the photosphere lies the lower atmosphere of the Sun, called the , and beyond that is the transition zone where the temperature of the atmosphere rises dramatically. The atmosphere of the Sun is extremely hot and is home to violent events erupting from the photosphere. A prominence is an ejected pillar of glowing gas extending thousands of kilometres from the solar surface. A prominence is visible in photographs and lasts for days or weeks. A solar flare is a more violent eruption from the photosphere that releases an enormous amount of energy. While a prominence will tend to follow the lines and loop back down to the photosphere, a flare will shoot off into space.

Extending far into space is a star’s corona, a hot and sparse upper atmosphere. The corona is very irregular in appearance, and it is believed that its shape is distorted by the eruption of prominences and flares. As the corona extends further from the Sun, it becomes the solar wind, a very thin gas of charged particles that travels through the solar system. Although the various levels of the Sun’s atmosphere cannot be seen except through a telescope with a special filter, the corona is visible when the solar disk is blocked by the Moon during an eclipse (explained in greater detail in module 3). The interior of the Sun is composed of gases made up of about three quarters hydrogen and one quarter helium. The density and temperature of the gas increases with depth beneath the surface. The regions just below the photosphere are known as the zone and the ; these regions allow heat and energy to travel out from the core to the surface. The core of the Sun is where nuclear fusion takes place, and is the energy source of the star.

Load Interactive Image Interior of the Sun

8. The Surface of the Sun

The Sun

The surface of the Sun was originally thought to be perfect and uniform, but we now know the photosphere is marked by numerous irregularly shaped dark patches called . Sunspots are depressed areas on the Sun that have a lower temperature than the surrounding surface. They are typically about the size of the Earth, and are composed of a darker central region called the umbra, which is surrounded by a lighter coloured ring called the penumbra. They are temporary features and constantly alter the appearance of the photosphere. Sunspots are closely tied to the solar magnetic field and often occur in groups or in pairs of opposite polarity. The rotation period of the Sun would be very difficult to determine without the aid of sunspots. Because the Sun is not solid, it experiences , meaning that the surface rotates at different speeds depending on , with the equatorial regions rotating faster than the polar regions. The number of visible sunspots varies to year, and the frequency follows a regular 11-year cycle between times of maximum and minimum. During times of maximum, hundreds of sunspots are visible, whereas during a minimum, the photosphere can be devoid of any sunspots. Complex groups cause the eruption of solar flares, which produce a substantial release of solar particles into the solar wind. Because charged particles from the Sun cause the aurora on Earth, the number of sunspots directly affects these displays. During a sunspot maximum like in 2001, we tend to see amazing auroral displays, and during minimums the aurora are essentially non-existent. Load Flash Applet Tracking sunspots

9. Studying the Sun and Stars

Because the Sun is so incredibly bright, we cannot safely look at it unprotected without damaging our eyes. However, the Sun can be safely viewed with the use of special filters or via projection. Filters can be fitted onto telescopes to block out more than 99.99% of the incoming light, leaving images astronomers can safely view and study. Various filters allow astronomers to observe different areas of the Sun, including sunspots and prominences. Image projection is a simple method that involves the projection of the Sun through a small telescope onto a piece of paper. This method does not show any of the solar atmospheres, but sunspots will be visible. We must never look directly at the Sun without safety precautions, but with them in place our star is a wonderful object to study.

Much of our knowledge of stars is obtained by studying our own star, the Sun. Astronomers have used complex mathematical models to investigate the solar interior, but observing the Sun in different wavelengths and with different filters can also give them valuable information. One of the most important methods in studying the interior of the Sun is called helioseismology, which involves observation of the “bubbles” on the photosphere as they rise and fall. The properties of these oscillating bubbles, combined with the mathematical models, reveal valuable information about the Sun’s interior. Because the Sun is an average star, we assume that the processes driving it will also be present in other similar stars.

10. Summary

Billions of stars populate our universe. The nuclear reactions within their core release incredible amounts of energy, and they would appear much brighter if it were not for their considerable distances. While looking up at the night sky, the only perceivable difference between stars is their , but stars each have their own characteristics. Although difficult to detect, stars shine different colours depending on their temperature. Spectroscopy is an accurate method of determining a star's colour, and will reveal the relative abundance of elements within its atmosphere. Many stars vary their brightness on their own, either due to their association in a double star system or due to unique processes within the star. Stars evolve through a life cycle that begins with their creation in an interstellar cloud. The cloud slowly collapses due to gravity, a protostar is formed and soon the internal temperature rises high enough to ignite nuclear fusion. A star processes hydrogen for the majority of its life before dying quietly as a planetary nebula or violently as a supernova. The Sun is in the middle of its hydrogen-burning stage, and will live another few billion years before dying.

The solar atmosphere is composed of three main layers: the chromosphere, the transition zone and the corona. Prominences and flares erupt into the atmosphere, releasing energy and particles into the corona and eventually extending into the solar wind. The Sun’s energy is generated within its core, and the internal regions transport this energy to the surface. The surface of the Sun is called the photosphere and is yellow and granular in appearance. Randomly covering the photosphere are dark patches cooler than the rest of the surface. These sunspots are temporary, and their numbers follow an 11- year cycle between times of maximum and minimum. They often occur in complex groups and are associated with the aurora on the Earth because they are the origin of solar flares. The Sun is an important object to study, but because it is so luminous it is extremely dangerous to look at the Sun without proper protection. The use of a special filter or the method of projection allows the Sun to be studied safely to better understand the processes within the stars. The Sun and the stars are incredible objects, and without them, life on Earth would not exist.

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AAVSO: Types of Variable Stars Page 1 of 7

AAVSO HOME > variable stars > types

Types of Variable Stars

Variable Stars Variable Stars are stars that vary in their light output. of the The origins of these light variations define the Season classification system of variable stars. Powerpoint Intro Stars Easy-To-Observe There are two kinds of variable stars; intrinsic in which Historical Light Curves variation is due to physical changes in the star or stellar Naming system and extrinsic in which variability is due to the Harvard Designation eclipse of one star by another or the effects of stellar Types rotation. Further Reading Impression of a Cataclysmic Var Acretion Disk Research: AAVSO in Print There are four main classes of variable stars. Within the intrinsic group of variables there are two classes: Image by Mark A. Garlick (http://sp Observing Manual pulsatingand eruptive. Within the extrinsicgroup there are two classes: eclipsing rotating stars. Below is a more thorough investigation of these four classes of varia Main sections of web The AAVSO Pulsating Variables Variable Stars Observing Access Data Publications Pulsating Variables are stars that show periodic expansion and con Online Store their surface layers. Pulsations may be radial or non-radial. A radia Education: HOA pulsating star remains spherical in shape, while a star experiencing radial pulsations may deviate from a sphere periodically. The follow of pulsating variables may be distinguished by the pulsation period Pick a star and evolutionary status of the star, and the characteristics of their p Click on image to show video. Create a light curve Recent Observations Cepheids (Period: 1-70 days; Amplitude of variation: .1 to 2.0 mag.) Find charts These massive stars have high luminosity and are of F spectral class at maximum, at minimum. The later the spectral class of a Cepheid, the longer is its period. Ceph a strict period-luminosity relationship. An example of a Cepheid variable light curve below.

http://www.aavso.org/vstar/types.shtml 4/2/2005 AAVSO: Types of Variable Stars Page 2 of 7

RR Lyrae stars (Period: .2 to 1.0 days; Amplitude of variation: .3 to 2 mag.) These are short-period, pulsating, white giant stars, usually of spectral class A. The and less massive than Cepheids.

RV Tauri stars (Period: 30-100 days; Amplitude of variation: up to 3.0 mag) These are yellow supergiants having a characteristic light variation with alternating shallow minima. Their periods are defined as the interval between two deep minima these stars show long-term cyclic variations from hundreds to thousands of days. G the spectral class ranges from G to K.

Long Period Variables (LPVs) (Period: 80-1000 days; Amplitude of variation: 2.5 to 5.0 mag.) These are giant red variables that show characteristic emission lines. The spectral range through M, C, and S. Also known as “Miras” after the prototype star.

Semiregular (Period: 30-1000 days; Amplitude of variation: 1.0 to 2.0 mag.) These are giants and supergiants showing appreciable periodicity accompanied by irregular light variation.

http://www.aavso.org/vstar/types.shtml 4/2/2005 AAVSO: Types of Variable Stars Page 3 of 7

Cataclysmic Variables

Cataclysmic variables (also known as Eruptive variables), as the n implies, are stars that have occasional violent outbursts caused by thermonuclear processes either in their surface layers or deep with interiors. Click on image to show video.

Supernovae (Period: none; Amplitude of variation: 20+) These massive stars show sudden, dramatic, and final magnitude increases as a re catastrophic stellar explosion.

Photograph of Before and After SN1987A Resized from the original photograph copyright of the Anglo-Australian Observatory (http://www.aao.gov.au/images.html).

Novae (Period: 1-300+days; Amplitude of variation: 7-16 mag.) These close binary systems consist of a , Sun-like star and a white They increase in brightness by 7 to 16 magnitudes in a matter of one to several hun After the outburst, the star fades slowly to the initial brightness over several years o Near maximum brightness, the spectrum is generally similar to that of an A or F gia

http://www.aavso.org/vstar/types.shtml 4/2/2005 AAVSO: Types of Variable Stars Page 4 of 7

Recurrent Novae (Period: 1-200+days; Amplitude of variation: 7-16 mag.) These objects are similar to novae, but have two or more slightly smaller-amplitude during their recorded history.

Dwarf Novae These are close binary systems made up of a Sun-like star, a white d an accretion disk surrounding the white dwarf. There are three sub-classes of dwar

U Geminorum (Period: 30-500 days: Amplitude range variation: 2-6 mag.) After intervals of quiescence at minimum light, they suddenly brighten. The duration outburst is generally from 5 to 20 days.

Z Camelopardalis These systems show cyclic variations, interrupted by intervals of constant brightnes “standstills”. These standstills last the equivalent of several cycles, with the star “stu brightness approximately one-third of the way from maximum to minimum.

http://www.aavso.org/vstar/types.shtml 4/2/2005 AAVSO: Types of Variable Stars Page 5 of 7

SU Ursae Majoris These systems have two distinct kinds of outbursts: one is faint, frequent, and shor duration of 1 to 2 days; the other (“superoutburst”) is bright, less frequent, and long duration of 10 to 20 days. During superoutbursts, small periodic modulations (“supe appear.

Symbiotic stars (Period: semi-periodic; Amplitude of variation: up to 3 mag.) These close binary systems consist of a red giant and a hot blue star, both embedd nebulosity. They show nova-like outbursts, up to three magnitudes in amplitude.

R Coronae Borealis (Period: irregular; Amplitude of variation: up to 9 mag.) These are rare, luminous, hydrogen-poor, carbon-rich, variables that spend most o at maximum light, occasionally fading as much as nine magnitudes at irregular inte then slowly recover to their maximum brightness after a few months to a year. Mem this group have F to K and R spectral types.

Eclipsing Binary Stars

These are binary systems of stars with an orbital plane lying near the line-of-sight o observer. The components periodically eclipse one another, causing a decrease in apparent brightness of the system as seen by the observer. The period of the eclips coincides with the of the system, can range from minutes to years.

http://www.aavso.org/vstar/types.shtml 4/2/2005 AAVSO: Types of Variable Stars Page 6 of 7

Rotating Stars

Rotating stars show small changes in light that may be due to dark spots, or patches on their stellar surfaces (“”). Rotating sta often binary systems. Click on image to show video.

Other Types of Variable Stars

The following types of stars are not recommended for observation by inexperienced due to either their irregularity, or the small amplitude of variation that they exhibit.

Flare stars Also known as UV Ceti stars, these are intrinsically faint, cool, red, main-sequence undergo intense outbursts from localized areas of the surface. The result is an incre brightness of two or more magnitudes in several seconds, followed by a decrease t normal minimum in about 10 to 20 minutes.

Irregular variables These stars, which include the majority of red giants, are pulsating variables. As the implies, these stars show luminosity changes with either no periodicity or with a ver periodicity.

The GCVS (General Catalogue of Variable Stars) classification of variable stars pro thorough description of the different types of variable stars.

z Outline of Variable Star Types

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